The same applies to certain industrial processes where the pressure inside the chamber in which the process is performed need not be as low as that, being as much as a few mbars, but where it is necessary to extract a certain flow rate of process gas while maintaining said pressure, since at said pressure the flow rate of a primary pump is very low and use is therefore also made of a pump assembly comprising a secondary pump and a primary pump. The primary pump and the secondary pump have their own respective drive motors.
The object of the present invention is to provide a unit pump assembly having a single drive motor and capable of delivering to the atmosphere while achieving a very high limiting vacuum at the suction end of down to 10.sup.-10 mbars.